On the Fossil Plants of the Coal-measures. 61 



vlously published figures and descriptions (Transactions of the 

 Literary and Philosophical Society of Manchester, third series, 

 vol. V. 1871) under the name of Vollcmannia Dawsoni. In the 

 present memoir he gives a detailed exposition of the various parts 

 of the plant, including the roots, rootlets, stems, branches, leaves, 

 and fruit, in different stages of their de\elopment. This is done 

 chiefly in t\^o modifications of the primary type — one from the 

 Lower Coal-measures of Oldham Lii Lancashire, the other from 

 those of Burntisland. Li its youngest state, the Oldham form 

 first appears as a mere twig, having a central fibro-vascular bundle 

 enclosed in a double bark. The vascular bundle consists entirely 

 of vessels which are chiefly, if not wholly, of the reticulated type. 

 When divided transversely, it presents a triangular section, the 

 triangle having long narrow arms and very concave sides. The 

 bark is already differentiated into two layers, and has its exterior 

 deeply indented by three lateral grooves — one opposite to each 

 concave side of the vascular triangle. The outer layer is prosen- 

 chymatous, with A'ertically elongated cells ; the inner one consists 

 of cylindrical parenchyma arranged in radial lines, the cells being 

 also elongated vertically. As the plant grew, successive vascular 

 layers were added exogenously to the exterior of the vascular axis. 

 Each layer consisted of a single linear row of vessels, which were 

 of large size opposite the concavities of the triangle, and small 

 where they approached its several angles. The radial arrangement 

 of those in the several growths \\'as equally regular ; they were 

 disposed in single radiating series, new laminre being intercalated 

 peripherally as the stem grew. These radiating laminae were sepa- 

 rated by small medullary rays. Omng to the fact mentioned, that 

 the laminfB radiating fi-om the concave sides of the central triangle 

 consisted of much larger vessels than those radiating from its 

 angles, three or four such growths sufficed to convert its conca\e 

 sides into slightly convex ones, whilst a few more such additions 

 converted the vascular axis into a solid nilindrical rod. At this 

 stage its transverse sections appeared definitely di\dded into six 

 radiating areas — three of large open vessels radiating from the 

 sides of the primary triangle, and three of small ones proceeding 

 from the sides and extremities of the angles. When these growths 

 have thus given a cylindrical form to the vascular axis, a change 

 takes place in its further development. Concenti'ic growths again 

 begin to form ; but in them all the vessels are of almost equally 

 small diameters : hence the abrupt termination of the three areas 

 of large vessels in the younger growths produces a distinct cir- 

 cular boundary line, marking a special stage in the genesis of the 

 stem. Ytoixv this point the additions go on uninterruptedly, the 

 vessels of each radiating lamina or A\edge increasing slowly in size 

 from within outwards as the stem advances towards maturity. 

 During these fin*ther developments the baric has continued to be 

 separated into two well-defiucxi forms. An inner layer consists of 

 very delicate elongated cells with square ends (prismatic paren- 

 ch}Tna) ; the.se are seen in the transverse section arranged in ra- 



